This invention relates to an apparatus for feeding slivers to a drawing unit of a fiber processing machine, particularly a draw frame in which the slivers are pulled from coiler cans by a withdrawing roll pair after they run through a plurality of supply rolls which are mounted on a sliver intake table and which have different circumferential speeds.
The slivers which are, by means of the roll pairs (supply roll and pressure roll) of the intake table, guided to a sliver drawing unit, enter the nip of the withdrawing roll pair in a state stretched about 1.05 times after they run on rider rolls. The intake draft equals the ratio of the circumferential speed of the rider rolls to that of the withdrawing rolls. In practice, the intake draft is set such that each sliver runs between the intake rolls and the rider rolls at the smallest possible tension, but without any snag.
In conventional arrangements the supply rolls have been driven, via transmission mechanisms (belts, sprockets, and the like) by the drive of the draw frame, that is, the motor which forms part of the drive for the drawing unit. In such arrangements the supply rolls have, as a rule, identical circumferential speeds. The slivers may often run at unlike tensions, for example, because of different distances between the supply rolls, on the one hand, and the intake roll pair, on the other hand. Since, however, the slivers which are only slightly twisted, are composed of loosely interconnected fibers, they are coherent only by virtue of the friction between the fibers and are not able to take up any mechanical tension stress without undergoing, at the stressed locations, an undesired elongation which may adversely affect successive processing steps.
It is a further disadvantage of the above-outlined prior art arrangement that while all the coiler cans at the intake table initially contain sliver quantities of equal length, often residual sliver quantities remain in some of the coiler cans, while others have already been emptied. In their travel path from the coiler can to the intake of the draw frame the slivers have to change direction several times. Since the locations of reorientation involve friction, forces are generated during the sliver travel which lead to unintended drafts as a function of the properties of the material and the free path lengths of the sliver between the coiler can and the machine. Such parasite drafts have a stationary and a non-stationary draft component. The stationary draft component leads to the above-noted non-simultaneous emptying of the coiler cans since the fiber processing machine pulls the slivers with a constant sliver speed rather than with a constant mass flow. The non-stationary component which is generated by the own dynamic properties of the sliver during the withdrawal process, leads to fluctuations in the number of the inputted sliver.
German Auslegeschrift (application published after examination) 1,115,624 discloses an arrangement in which the supply rolls, dependent on their distance from the drawing unit, have different diameters and, accordingly, different circumferential speeds. The different circumferential speeds decrease as the distance from the drawing unit increases so that a slippage between the slivers and the supply rolls as well as a sagging of the sliver between successive supply rolls is compensated for and thus the slivers, upon entry into the withdrawing roll pair of the drawing unit have, with a good approximation, identical tensions. In this arrangement the supply rolls which are closest to the drawing unit have--assuming an identical rpm for all supply rolls--larger diameters than the more remote supply rolls. All the supply rolls are driven by a common drive shaft. It is a disadvantage of such a prior art arrangement that an adaptation of the intake tension between successive supply rolls is not possible as the operational conditions change. It is a further drawback that the slivers have only approximately the same tension.